Capital Stock Capital Stock (Details) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Feb. 25, 2019	Mar. 31, 2019	Dec. 31, 2018	May 08, 2017
Subsequent Event [Line Items]
Shares of common stock authorized (in shares)		100,000,000	100,000,000
Shares issued and outstanding (in shares)		49,900,000	49,700,000
Maximum shares allowed for issuance (in shares)		2,000,000
Par value (in dollars per share)		$ 10
Stock repurchase program amount				$ 200,000,000
Stock repurchase program remaining amount		$ 106,000,000
Stock repurchased and retired during period, shares		610,177
Stock repurchase program amount used		$ 43,500,000
Average price per share (in dollars per share)		$ 71.22
ASR December 2018
Subsequent Event [Line Items]
Accelerated share repurchased payment			$ 50,000,000
Stock repurchased and retired during period, shares			700,000
ASR, initial price per share (in dollars per share)			$ 71.43
ASR February 2019
Subsequent Event [Line Items]
Stock repurchased and retired during period, shares	37,387
ASR, final price per share (in dollars per share)	$ 67.81